The invention relates to a procedure for controlling an exhaust gas purification system of a combustion engine, consisting of one or several catalytic converters for converting and/or storing at least one exhaust gas component of an exhaust gas of the combustion engine, which are arranged in an exhaust gas duct of the combustion engine, whereby at least one of the catalytic converters represents an oxidization catalytic converter. The invention furthermore relates to a device for implementing the procedure according to the invention.
In order to achieve a reduction of ecologically harmful exhaust gas components in exhaust gases of combustion engines, it is established to arrange catalytic converter systems with at least one catalytic converter in an exhaust gas duct of the combustion engine. Depending on the type of the catalytic converter the catalytic converter causes a conversion of one or several exhaust gas components, such as uncombusted hydrocarbons (HC), carbon monoxide (CO) and nitrous gases (NOx), into more ecologically relevant products. Furthermore catalytic converters are familiar, which have storage components, which are able to absorb certain pollutants. Thus NOx storage catalytic converters are in particular used at lean-loadable combustion engines, which absorb in lean operating phases with λ>1 NOx and which carry out a reduction of the stored NOx with λ<1 in interconnected rich regeneration phases.
More or less strong interruptions of conversion and/or storage activities as opposed to an original activity of the catalytic converter occur practically at all catalytic converter systems during the operation. The activities with regard to a conversion or storage of different pollutants can thereby decline by different amounts. Diverse damaging patterns are in particular known at NOx storage catalytic converters, which for example cause a significant deactivation of the NOx volume at a still good HC-conversion. Likewise however an exactly contrary damaging behavior is also known.
Stricter laws in the area of diagnosing emission relevant components require the controlling of all exhaust gas after-treatment components in the range of the on-board-diagnosis (OBD) as well as the used sensor system on OBG-threshold values, which are mostly stated as a multiple of the emission threshold value. Especially the controlling of the catalytic converters is a big challenge.
According to the state of the art a number of different diagnosing procedures of exhaust gas after-treatment systems are already familiar.
DE 41 12 478 C2 for example describes a procedure for assessing the ageing status of a catalytic converter, at which the lambda values are measured in front of and after the catalytic converter. It is examined whether the lambda value behind the catalytic converter shows a corresponding transfer during a regulating oscillation in front of the catalytic converter from rich to lean or reverse, and then, if that is the case, the gas mass flow that runs through the catalytic converter is determined, the temporal integral of the product of the gas mass flow and lambda value in front of the catalytic converter is calculated, the temporal integral of the product of the gas mass flow and lambda value behind the catalytic converter is calculated and either the difference between the two integrals or the quotient of both integrals or the quotient of the difference and one of the two integrals is used as a measure for the ageing status of the catalytic converter. The disadvantage of the described procedure is that the lambda value in front of the exhaust gas purification system has to be measured with a complex wideband lambda probe, in order to determine the inserted or extracted oxygen amount via the integration of the product of the actual lambda value and the gas mass flow.
DE 198 03 828 A1 describes a procedure as well as a device for controlling an exhaust gas catalytic converter at combustion engines, at which the oxygen content of the exhaust gas after the catalytic converter is determined and at which the average oxygen content of the exhaust gas in front of the catalytic converter is shifted in a direction which leads away from the previously determined oxygen content after the catalytic converter and at which the change of the oxygen filling level of the catalytic converter that results from the change of the average oxygen content is determined and compared to a predetermined threshold value and at which an error message is remains undone if the predetermined threshold value is exceeded before the oxygen content of the exhaust gas after the catalytic converter changes.
DE 10 2006 041479 A1 describes a further procedure for determining the oxygen storage capacity of an exhaust gas purification system for a combustion engine, at which a difference amount between an oxygen amount that is entered into the exhaust gas purification system and an oxygen amount that is emitted from the exhaust gas purification system. It is enabled to begin a measuring cycle even at a catalytic converter that is not completely emptied of oxygen or filled with oxygen and to state whether the catalytic converter provides a sufficient conversion capability. Furthermore an average of oxygen can be considered at a not completely filled exhaust gas purification system, the so-called slip.
Current requirements regarding an on-board diagnosis, as they are know from the USA, require for example a controlling of oxygen catalytic converters, for example diesel oxidization catalytic converters (DOC), of their capability to provide a suitable gas composition, a so-called “feed gas”, for subsequently mentioned exhaust gas after-treatment systems. The focus is currently on the provision of a defined NO/NO2 relation, so that the NOx reduction in the subsequent SCR catalytic converter can run optimally. SCR (selective catalytic reduction) means the technique of the selective catalytic reduction of nitrous gases in exhaust gases of firing systems, waste incineration plants, gas turbines, industrial plants and engines. The chemical reaction at the SCR-catalytic converter is selective, which means that preferable nitrous gases (NO, NO2) are reduced while undesired side reactions (as for example the oxidization of sulfur dioxide to sulfur trioxide) is mostly suppressed. There are two types of catalytic converters. One type basically consists of titan dioxide, vanadium pentoxide and tungsten oxide. The other type uses zeolites.
One requirement relates to a controlling of the coating of a diesel particle filter (DPF) of its capability to oxide uncombusted carbon monoxides (HC).
But with the currently available procedures it is not possible to fulfill all requirements for a controlling. Thus it is for example not possible to evaluate the NO oxidization capability of a diesel oxidization catalytic converter (DOC) with the aid of the HC conversion capability, because the NO oxidization capability declines faster, which means “ages”, and therefore there is no suitable correlation of the two characteristics. If one tries on the other hand to control the DPF-coating with the exothermic procedure known from the diesel oxidization catalytic converter (DOC), one fails because of the too low HC amount, which still achieve a diesel particle filter (DPF) that follows the diesel oxidization catalytic converter under normal circumstances.